Photographic developer



Patented Dec. 5, 1939 PHOTOGRAPHIC DEVELOPER James R. Alburger, Merion, Pa., assignor to Radio Corporation of America}, a corporation of Delaware 9111 Application November 30, 1938, Serial No. 243,23!

3 Claims.

This invention relates to photographic developers and methods of photographic development, and is an improvement on the developer of my application Serial No. 205,363, filed April 30, 1938, entitled Photographic developer.

it has heretofore been customary to develop sound record negative film in ordinary positive developer or in a modification thereof, thereby producing a negative having the same relative characteristics as a picture positive or having these characteristics very slightly modified. This procedure has been highly undesirable, particularly with variable area sound records, where an extreme density of the exposed area is desired,

le together with complete freedom from fog in this purpose must be satisfactory for use in the tanks of continuous developing machines; it must have a' relatively long life, i. e., must not age too rapidly; and it must maintain its developing action substantially constant during its period of usefulness.

Heretofore, no developer has been available having the foregoing characteristics. My improved developer has all of the foregoing characteristics and, in addition thereto, is extremely inexpensive, decreasing the developer cost, per foot of film, to only a small fraction of the previous cost.

In the preparation of my improved developer, I make use of the peculiar characteristic of certain metallic salts which permits them to act as a buflfer and to maintain the effective alka- Another object-of my-invention is toprovide an improved high contrast developer.

Another object of my invention is to provide a developer having a relatively long life without replenishment; 1

Another object of, myinvention is to provide Another object of my invention is to provide a developer which will give a surface image.

Another object ofmy invention is to provide a developer which will produce a very uniform grain structure in the image.

Another object of my invention is to provide a developer which will prevent clumping of the silver grains.

Another object of my invention is to provide a developer which will give better definition and higher resolving power than it secured by previous developers.

Another object of my invention is to provide a developer which has substantially constant developing effect during its entire life.

Another object of my invention is to provide a developer which has a lower change of development time with change in temperature than has heretofore been secured.

Another object of my invention is to provide a developer adapted for use in continuous developing machines whereby the addition of fresh developer of the original composition at the rate at which developer is removed bythe film will exactly balance both the exhaustion and oxidation of the developer remaining in the machine.

Another object of my invention is to provide a developer which prevents softening of the gelatine by alkali.

Another object of my invention is to provide 85 The objects are accomplished according to my invention by adding a metallic compound, such, for example, as potassium alum, to the developing solution, and using an alkali in sufficient quantity to dissolve or redissolve the precipitate which tends to be, or is, first formed.

My invention, in its broad aspect, applicable to developers containing practically any of the usual developing agents which function in alka line solution, and also is adapted to the use of any of the usual alkalies, although some developing agents and some alkalies are preferable to others. In the present instance, I use hydroquinone as the developing agent and a mixture of solution hydrate and carbonate as alkali.

For example, a very rapid developer is necessarily quite alkaline. In order to produce a proper buffering balance of the alum in this highly alkaline solution, it is accordingly necessary to use a large quantity of alum. Under this circumstance, if a sodium carbonate, for example, is used exclusively as alkali, the total solids in the solution become extremely great, in order to maintain the same constant alkalinity in the manner described in detail hereinafter, and I therefore prefer to use a large proportion of sodium hydrate, with a certain portion of the carbonate to decrease the rate of change of alkalinity due to the efiect of air.

Although I have above referred to the use of alum in developer, I find that a number of other materials may be used. The aluminum, for example, may be introduced in the readily available form of potassium aluminum sulphate, known generally as alum, or any other convenient water soluble aluminum salt may be used, such, for example, as aluminum sulphate, aluminum chloride, or aluminum bromide.

The aluminum compounds produce sufiicient tanning action on the gelatine, or prevent the softening action of the alkali to such an extent, that I have found it practical to use the developer including aluminum up to a temperature of well over 105 F., at which temperature the developer becomes very uncomfortable to handle. As compared to this, previous developers containing an equivalent quantity of developing agent and alkali completely remove the emulsion from the backing at a. temperature'as low as 80.

In the preparation of my improved developers, I used somewhat less than the usual proportion of sodium sulphite for the reasons that, first, a large quantity of sulphite is not necessary and, second, the reduction in quantity of sulphite decreases the solution of silver salts and redeposition thereof which produces diffusion of the image in developers high in sulphite.

The sodium hydroxide is balanced with an appropriate amount of alum determined as follows: Powdered alum is slowly added to the solution containing hydroxide. As addition of the alum is continued, the rate of solution slowly decreases until the point is reached where further addition of alum produces no further solution, leaving undissolved alum crystals. Conversely, the alum may be dissolved first and the sodium hydroxide added later. In this case, the initial addition of sodium hydroxide produces a-precipitate of aluminum hydroxide which is redissolved on further addition of sodium hydroxide, and when this precipitated aluminum hydroxide is just redissolved the solution is in proper equilibrium. The appropriate amount of potassium bromide may be added to the solution at anytime during preparation thereof.

The following formulae illustrate a satisfactory composition which Ihave used:

Sodium sulphite grams Hydroquinone do 20 Sodium carbonate ..do .12 Potassium bromide use. d 2 Sodium hydroxide do 30 Potassium alum (crystal) do 40 lllh'iter c c-.. 1000 A second formula is as follows: Sodium sulphite grams 50 Hydroquinone do 15 Sodium carbonate -do 80 Potassium bromide do 9 Sodium hydroxide do 30 Potassium alum do.. 40 Water c. c.. 1000 The first of the foregoing formulas is particularly adapted for use in closed systems :where the developer is not unduly exposed to air, either in the developing machine, thesettling or supply tanks, or the conduits therebetween.

The second formula is of more general utility and is considerably more flexible in composition. In the second formula, the total permissible variation of sodium sulphite ranges from zero to saturation which occurs at about 140 grams to the liter. At low quantities of sufphite, the developer oxidizes too rapidly, while, at about 80 or 90 grams per liter, it exerts undesirably large solvent action on the silver salts in the emulsion. The practical limits of variation of the sodium sulphite range from about 30 to 70 grams per liter, with the most desirable value being that given in the above formula. The hydroquinone may be varied in accordance with the activity desired in the developer, but the value of 15 grams per liter is the most satisfactory for use in filmdeveloping machines. The practical range of variation of hydroquinone is from 12 to 18 grams per liter or a variation of about 3 grams per liter in either direction. The sodium carbonate may be varied from '60 to 90 grams per liter, as a practical matter, but, in any quantity, it has the eifec't of'materially decreasing the rate of oxi-- dation of the developer, as compared to developer without the carbonate, the value of 80 grams being the most satisfactory. The potassium bromide may have any value from 2 to 10 grams per liter, but between 8 'and' 10 grams per liter has the most stable efiect with a minimum of variation in effect due to increase in bromide concentration during development. The sodium hydroxide and alum must be maintained in a ratio of 3'to 4 within about 3%, but, so long as this condition is maintained, the sodium hydroxide may vary from 10 to 60 grams per liter with operative results, although the practical limits are between 25 and 35 grams per. liter with the alum varied in proportion.

Where the ordinary types of metol-hydroquinone developers heretofore used are effective for approximately 20 feet of film per liter of developer, with appropriate replenishment ofithew developer in the meantime, my improved developer will serve to develop'approxim'ately 250' the prior developers used on sound film which, I

with the customary exposure, would develop the film to a, density of the order of 1.9, my improved developer will produce a density of approximately 2.1 on the sound negative, and the sound prints can be exposed and developed to the correspondj lution is an excess of NaOH. The presence of processing, by J. 0. Baker and D. H. Robinson, Journal of the Society of Motion Picture Engineers, volume 80, No. 1, January, 1938. Further, the high frequency loss, for example at 9000 cycles, with my developer is no greater at these high densities than at the lower densities attained with the prior art developers.

The film footage per liter above referred to is such that no replenishment of the developer is required in ordinary film developing machines. The film runs through the machine at a speed of the order of 180 feet per minute, and a compressed air jet is used to blow adhering developer from the film back into the tank. In spite of this jet, a certain amount of developer adheres to the film, and this residual adhering developer is a quantity of the order of magnitude of the developer used in developing the film. By adjusting the pressure on this compressed air jet or blow-back, the rate of carry-over of the developer may, if desired, be made substantially identical with the rate of exhaustion of developer. If fresh developer is then added to the tank at such rate as to retain the fluid level constant, the developing solution will reach a state of equilibrium which will be thereafter maintained.

Both of the foregoing developer formulas have the advantage over the developers described and claimed in my aforesaid application Serial No.

- 205,363, in that the oxidation rate is materially lower than with those prior developers. In fact, the sum of the oxidation rate and the rate of exhaustion in a reasonably closed system are substantially identical with the rate of carryover of the developer by the film. The developer can, therefore, be maintained at a uniform strength by adding fresh developer so as to maintain the fluid at a constant, level.

Operation of we developer The reaction of the organic reducing agent with the exposed silver bromide in the film produces a shift in ion concentration through a long chain of reactions. When the developer is oxidized by silver bromide, Brions are released. Aluminate ions exist from the reaction of ZKAKSOOrQ-BNBOHL';KisO4+3NE2SO4+ 2Al(OH)a ;Al(OH)a+NaHL'5NaAl01+2Hz0 It is understood that each and every compound indicated in the above reaction will form certain ions in solution. For example, the alum in solution would produce potassium ions, aluminum ions and sulphate ions. The sodium aluminate in- .dicated would, in solution, produce sodium ions and aluminate ions. It is evident from the above reaction, which is really a mass reaction balance consisting of three reactions, that there will.be.

presentin the'solution a large number of different ions. t v om chemical functions known to the art, it

Brions would shift the balance of the above reaction slightly to the left. AHOYI): is now better able to combine with the gelatine of the film to harden it, as in any tanning action. Thus the film (gelatine) in the near neighborhood of the developed image undergoes a pronounced hardening which is evidenced by a distinct lack of swelling of the gelatine.

As the supply of free alkali is converted into salts in course of development, free alkali is liberated by the aluminum-alkali compound or complex, thereby maintaining the alkalinity effectively constant. At the same time, the aluminum hydroxide which is freed forms a gelatinous precipitate which entraps exhausted developing material and other foreign material which may be in the developer and carries all of this suspended material out of the solution in the manner well known in water purification by the use of aluminum salts. The developing solution is thereby maintained at all times free from the exhausted material which tends to form scum, spots, stains or fog on the film in the developers of the prior art.

This coagulation of aluminum and deleterious material may be either permitted to settle to the bottom of the developing container and removed therefrom at convenient intervals or the developer may be passed into a separate settling tank or container from which the sediment may be'removed from time to time. Since the addition of fresh developer of the original composition does not tend to redissolve the aluminum as the addition of a stronger solution, such as generally used for enrichment of developer, would do, this precipitate does not tend to become finely divided or redissolved, and it is therefore readily removed from the zone of operations in the manner before described. I This greatly decreases the cost of operation of developing machines as compared to the present procedure wherein the developer is filtered under high pressure and through complicated filtering mechanisms in order to remove exhausted developing material. Of course, with my improved developer and method of development, a filter may be used if desired, but the filter required, due to the large size and gelatinous nature of the material to be removed, is very much simpler than that required for removing the fine suspended particles from the usual commercial types of developer.

A further advantage of my improved developer is that if the aforesaid gelatinous precipitate is not removed, but is kept in suspension in the solution by mechanical agitation, either through the passage of the film through a relatively small quantity of solution or otherwise, this gelatinous precipitate does not show the tendency to adhere to the film, which is common to the materials in suspension in a partly exhausted developer of the usual type. In other words, any such material is removed from the film by the blow-back and any residual material which may adhere to the film is easily removed in the rinse water, leaving no Sodium sulphite 50 I20 Hydroquinone 15: 5' Sodium carbonate r. 80:10 Potassium bromide 8: 2 Sodium hydroxide 301-20 Potassium alum .l 40:25

Sodium sulphite 50:20 Hydroquinone 3 10 Sodium carbonate 80:10 Potassium bromide 8i- 1 Sodium hydroxide 5 Potassium alum 5 the ratio of sodium hydroxide to potassium aim being substantially three to four.

3. A photographic developer having substantially the following composition per-liter of water solution:

Grams Sodium sulphite Hydroquinone 15 Sodium carbonate Potassium bromide 9 Sodium hydroxide; 30 Potassium alum '40 JANIES R. ALBURGER. 

